A vestigial sideband ("VSB") receiver is a high-definition television ("HDTV") receiver in the United States which has been proposed by the Advanced Television Systems Committee ("ATSC"). Many television receivers (including the VSB receiver) detect data with only a one-dimensional signal of an in-phase ("I") channel, whereas other demodulators demodulate a digital modulated signal. When the phase of the data signal received by a VSB receiver is not properly corrected, the decoding operation of the receiver is degraded.
Accordingly, a conventional phase correction circuit has been developed which includes an error tracking loop to overcome the problems described above. The correction circuit transforms a one-dimensional input signal into a two-dimensional signal (I) and (Q) by generating a quadrature ("Q") signal component to more accurately correct the phase of the input signal. Also, the correction circuit performs the phase correction operation on the input signal in a closed loop feedback manner using a decision error. The above phase correction circuit is described in the U.S. Pat. No. 5,406,587 which is assigned to Zenith Electronics Corporation and which is incorporated herein by reference.
The phase correction circuit or phase tracker disclosed in the above-referenced patent is illustrated in FIG. 1A, and includes a multiplier 22, a delay 24, a Hilbert transform filter 30, an adder 26, a complex multiplier 28, various look-up tables (32, 34, 42, 48, 50, 52) and other known components. The multiplier 22 controls the size of a one-dimensional input signal to produce a controlled input signal, and the delay 24 and Hilbert transform filter 30 transform the controlled input signal into a two-dimensional signal. The adder 26 removes a residual direct-current component of the input signal, and the complex multiplier 28 corrects the phase of the input signal and outputs a Q signal component of the input signal. One of the look-up tables detects a decision error component in the input signal for performing the phase correction operation, and other look-up tables output a corrected value based on the Q signal component output by the complex multiplier 28. The corrected value is fed back to the multiplier 28 and the adder in a closed loop in order to correct amplitude errors of the input signal.
When an input signal is a one-dimensional signal, the phase of the signal can be adjusted to either a normal phase or an antiphase. (See FIG. 1B). In such a situation, the I-channel data includes information which is actually transmitted, and the Q-channel data is not actually transmitted but serves to reduce a frequency spectrum of a modulated signal of the input signal. Accordingly, when a phase error is generated during the demodulation of the input signal, the I-channel sampling data includes both the I-channel data and the Q-channel data. Thus, the phase tracker also needs information relating to the Q-channel data in order to correct phase errors, and such information can be obtained by filtering the I-channel data via the Hilbert transform filter 30.
When the phase errors of a one-dimensional input signal are corrected using only an error component generated by decision, locking into an antiphase component necessarily occurs. Thus, every phase correction circuit that receives a one-dimensional input signal requires an additional process for antiphase correction. The phase tracker disclosed in the above-described patent application can solve the above problem because the antiphase state of the input signal is corrected if a constituent for obtaining a phase error component using a predetermined signal is additionally provided. However, in this case, the circuit configuration of the phase tracker is very complicated. Also, the phase tracker requires an excessive rotation with respect to a phase error of at least 90.degree. and thus, causes a slow initial convergence speed. Furthermore, the multiplier described in the above-referenced patent may perform unstable automatic gain control ("AGC"), and therefore, the performance of the entire system may be deteriorated.